Understanding alpha-stabilized defects in titanium ingots, is of continuing interest to both titanium producers and aircraft engine manufacturers. Alpha defects are interstitially stabilized regions of substantially higher hardness than the surrounding normal material. They arise from a high local concentration of nitrogen with or without oxygen which increases the beta transus temperature and produces a hard, brittle region rich in the alpha phase. These defects are sometimes called high interstitial defects (hids) or low density inclusions (ldis). The term ldi arose from the observation that these defects are usually associated with a void or voids in the microstructure; the alpha-rich phase itself, however, is not of low density. These defects have acted as fracture sources or crack initiation sites in fan or compressor disk failures. To diminish the occurrence of these failures, several previous studies have focused on understanding of the formation and elimination of type 1 hard alpha defects. As part of a cooperative program with the general electric company, research at the Bureau of Mines has been undertaken which: evaluates the Bureau's induction slag melting (ism) process as a method of causing dissolution of hard alpha defects versus commercial consumable electrode vacuum are melting (cvar); compares the rate of dissolution of hard alpha defects in a single melt (ism vs cvar); determines the detectability, by ultrasonic inspection, of hard alpha defects; and characterizes the defects found using metallographic techniques.
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